Can be replaced on the road. I replaced my original Gen2 old style with a new style before our long trip this year. The old style relied on a small ball bearing which had a slow leak in it. The dealership forced me to purchase through them (I had no 5th wheel hitch to take delivery - just factory puck system) and I was never happy with the install or the Goosebox I received. The new relief valve blew out pulling out of fuel stop in Ohio (it was a very awkward drainage dip that I had to cross). I was only two miles from destination and put the old relief valve back in and it held air for the first time for the next 4K miles. Pulled into a temporary site in NC and heard the pop and the ball bearing had blown out. Again, a very awkward position where I had to pull off the road and onto grass and over about a 3" rounded curb when that happened. Found a local truck repair/tow shop in Aberdeen NC and they fixed me up with a DOT approved line with a Schrader valve on the end so I could fill the bladder - standard truck air-brake parts. That is still holding air and I'll probably leave it until we get out to GD's repair facility in April where they will be checking for excessive flex in the cross frame where the wings are attached to.
If you order the Goosebox now, you will probably get a Gen3 with the newer style relief valve. I have no problems driving with either - pulls smooth, almost no chucking, and no hitch in the truck - just a gooseball. If there was any knock on the Goosebox (very few), it was pressure loss with the old style relief valve but I would buy it again. Pictures below.
Old style
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New style replacement
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