Tony - We camp every year in KY a couple times each year for about 10 years now - either as a destination or a way-point. I recommend the Kentucky Horse Park CG as well - it's a great CG and perfectly located. They book up in my experience so go online and get a res. I have seen 45' motor-homes in there so no worries. Alternately, you can camp in the primitive area (basically a field adjacent to the CG) and access the KHP facilities - but there is no water hookup and you need a geni. I actually prefer the primitive area for short stays.
I also recommended Taylorsville Lake State Park. It's a little "off" the bourbon trail, but it's one of our favorite spots. Lake, pontoon rentals, hiking trails, horseback riding, etc. You might want to check it out. I have seen some pretty good size rigs in there, but call and they can likely tell you what sites will fit your set up.
If you are going to Mammoth Cave I can tell you the MCave CG sites will be too tight for your 5th. Typical national park - not designed for the modern rvs. I jammed my 36' travel trailer in one of the sites but there were very few if any that I recall that could take a full size 5th. There was a nice little CG called Cave County Campground in cave city. Sites were plenty big, but it's really just a overnight CG or a place to lay your head at the end of the day. Nice owners that I recall, but right off the highway so was pretty noisy. There were some other CG options between Cave City and the park, but we have not stayed in any of those.
Kentucky in the spring is awesome - enjoy.
