Replacement King Mattress

[gobama84]

Mattress Insider can even make one this shape.

[N&M_Weaver]

Thanks, will look into them.

[pasnyu]

I have a 399TH as well and replaced the mattress with a Tuft & Needle king size mattress. I did the same as someone mentioned above and cut the mattress to fit the awkward turn radius at the head of the bed. I created a template out of cardboard for the turn. Then I removed the cover of the mattress and cut to the template. Since the mattress is all foam, it's very easy to do.

[SoCalMoto]

Update #2

I called Grand Design to confirm the King mattress dimensions and was told they were 70 x 80. However, after removing the stock linens, I discovered the mattress is really an angled King mattress with some bizarre dimensions. In order to make it fit up against the front cap, the stock King mattress has a rounded corner in the upper-left and a sharp angle in the upper-right (see image). I took some really quick and dirty measurements (see image).

I had already ordered a custom 70 x 80 mattress from a local Banner Mattress store and it could not be returned (see images). Luckily, things worked out OK. The custom 70 x 80 mattress leaves a small gap at the top of the bed, but it's not large enough to let a King size pillow fall through. Along the foot of the mattress, there is about a 4-5 inch overhang but it is so small it's almost impossible to notice. The most noticeable thing is the height of the new mattress - it's thick! I purchased their higher-end mattress ($2700) and after sleeping on it for a night am really happy with the purchase.

Hope this helps someone!

Cheers, Garo

[LogicDog]

Update #2

I called Grand Design to confirm the King mattress dimensions and was told they were 70 x 80. However, after removing the stock linens, I discovered the mattress is really an angled King mattress with some bizarre dimensions. In order to make it fit up against the front cap, the stock King mattress has a rounded corner in the upper-left and a sharp angle in the upper-right (see image). I took some really quick and dirty measurements (see image).

I had already ordered a custom 70 x 80 mattress from a local Banner Mattress store and it could not be returned (see images). Luckily, things worked out OK. The custom 70 x 80 mattress leaves a small gap at the top of the bed, but it's not large enough to let a King size pillow fall through. Along the foot of the mattress, there is about a 4-5 inch overhang but it is so small it's almost impossible to notice. The most noticeable thing is the height of the new mattress - it's thick! I purchased their higher-end mattress ($2700) and after sleeping on it for a night am really happy with the purchase.

Hope this helps someone!

Cheers, Garo

Thank you for this sketch! We are using it for a custom mattress in our 2020 351m. Your post was very helpful.

[chunker]

It seems the "RV King" is the latest rage and frankly I hate any mattress with the term RV applied to it. First typical RV stuff is crap and wears out faster than the joy of having an Easter duckling. My last few RVs have had real queen, 60x80, which for us works better. When, not if, that new mattress collapses I can go to any mattress store, Sams, Costco, etc and get a superior replacement for a fraction of the cost of one of those "RV" types. Second I can get properly fitting sheets/bedding for the mattress instead of having to buy at an RV dealer or specialty shop. Since RV mattresses have no "box springs" and just typically sit on a plywood platform, a properly aimed saw can make that useless "king" platform into a proper real queen base.

Maybe you guessed it but a good nights sleep is important to me and having my butt, shoulders, or other parts bottom out on a typical RV POS mattress isn't fun. Bed replacement and potential alteration is one of the first changes I'll make along with putting a safer stronger suspension under it. That helps me sleep better too.

[Dive Bar Casanova]

We have the "Short Queen" AKA RV Queen. With past RV's we tried the home type mattresses but they are way too heavy to use the underbed storage. But a better mattress.
Primo makes a good one about $300 delivered from Sit n Sleep. It's flexible enough for the underbed storage to articulate mid-mattress, get around the corners to install and fits perfectly, and it's comfortable, but heavy.

Wife is 5'11 and 110 lbs and her side of the stock Momentum mattress bottomed out and stayed that way from day one.
So, new RV and we're back at it with mattress issues.

[chunker]

We have the "Short Queen" AKA RV Queen. With past RV's we tried the home type mattresses but they are way too heavy to use the underbed storage. But a better mattress.
Primo makes a good one about $300 delivered from Sit n Sleep. It's flexible enough for the underbed storage to articulate mid-mattress, get around the corners to install and fits perfectly, and it's comfortable, but heavy.

Wife is 5'11 and 110 lbs and her side of the stock Momentum mattress bottomed out and stayed that way from day one.
So, new RV and we're back at it with mattress issues.

Which Momentum do you have? I thought GD used real or residential queen, 60x80, in the Momentum. I haven't looked at the "G" class so maybe that. Reference the under bed storage. There typically are gas springs/struts attached to assist the lifting of the platform. Upgrading the strut to a higher rating might help the lifting. The strut will have about a thousand markings but eventually you'll be able to find the brand and PSI rating. The ball and socket ends can be popped off for removal. You'll need to brace the platform up to make it easier. Since the stock mattress is a lightweight POS, I would just set it off to the side. Trying to determine what higher gas spring rating is needed would be a trial and error effort or if you have a spring scale like what they measure larger fish, you could try that with the stock mattress on, divide by 2 and compare with stock spring rating. Then with new mattress on weigh, divide by 2 and swag it to come up with an appropriate upgraded spring rating.

You'll obviously need to make sure the spring length is the same and possibly reinforce the attaching points for the springs to accommodate the higher force exerted. Frankly it's a shame to have to go that route just because the manufacturers are too cheap to install something better. Lousy mattress quality is maybe the oldest known fault in an ever declining quality of the RV product.

The springs can be purchased at RV dealers, most auto parts stores, online of course. I don't use or access the under bed storage that much so getting to stuff there isn't that big an issue for me. But I feel your pain literally with that mattress.

EDIT I remembered that springs are rated for pounds not PSI so that can make an upgrade easier. If the stock are 50 pounds, upgrade to maybe a 70 and try that. My GFs Crusader has an outdoor kitchen and the kitchen door is held open with 2 springs of 40# rating. Door wouldn't stay open and I got tired of bracing it open when I cooked crabs on the stove. I couldn't find that spring so went with 2 50#s and it worked well.

[Dive Bar Casanova]

Yeah the pistons will have to be replaced with HD or several bad things happen.