I've seen these in person and they are longer than 3 feet, more like 4 but definitely not one to stretch your legs out in.
I don't care if my legs hanging outside the tub, just as long as I can soak the lower part of my back in hot water. The pain does not get real bad very often but it would be nice to soak in hot water if I really was in a lot of pain.
I once read that studies have shown that most accidents occurr within 10 miles of home, so I moved
DOn't let the small water heater stop you. Boil a pan of water, and add that to the tub once it has more than a couple of inches of water in it, and that will warm up the coolish water that will fill the tub. And remember that the RV water heater is 140F, so mixed with 60F water 50/50, you end up with about 11 gallons of 100F water.
And RV water heaters recover fairly quickly, so if you don't have any water run into the tub for about 10 minutes, the water heater can recover from 100F to 140F in that time, just in time to add more hot water to keep the tub warm.
What I might do is using the outside shower, fill the fresh water tank with 6-10 gallons of hot water, then using the pump, if the fresh water tank is above 80F, you can fill the tub with plenty of hot water, or take a longer shower without running out of hot water.
It sure was nice camping in a Country COach, with a 10 gallon water heater. It never ran out of hot water! Some new water heaters use a 160F thermostat, and a mixing valve. The mixing valve mixes the super hot water with cold water, so output is limited to only about 125F, then you can get many more than the standard 6 gallons of water out of the 6 gallon tank.
I have a very small tub/shower. I like that it is a tub, even though I have no chance of sitting in it. I can soak my feet if I ever wanted too, and it works for kids less than 3' tall, the larger ones can take a shower. I can plug the drain, and using a dishpan move some water into the black tank, it is 59 gallons in my RV, while the grey is only 42. My fresh water is 100, so when dry camping in Yosemite, it is handy to move some more water into the black tank.
I am glad that I don't have a standard 3" deep shower pan. I have overfilled the grey tank a few times, and if coming down a mountain with a full grey tank, it can sometimes flow up the drain into the tub, no problem in my case, it will all drain back on the next curve. But with a shower pan, it might not drain back, or will splash onto the floor.
You can always run the hotwater heater on gas and electric if capable. The recyle time is pretty quick from my experience. I have seen inflatable hot tubs on Amazon for around 500.00. They run on 110V and weigh about 70 pounds when disassembled. This could be an option as opposed to a tub in the fifthwheel. Plus it seats TWO! May not be an option for the winter months but a thought anyway.
2003 Chevrolet C3500, CC, LB, Duramax/Allison
2004 Coachmen Somerset 318RLTS
The tub in our Komfort is where the litter box goes, when the kitties travel with us. :-)
2002 GMC Sierra 2500 HD Duramax Crew Cab 4x4
Banks Bullet Tuner and Monster Exhaust
B&W Turnover Ball with 5th Wheel Companion
2004 Komfort 25FSG Fifth Wheel
1936 John Deere Model A
International Flying Farmers 55 Year Member
Watch out for that clumping cat litter down the drain, sure wreaks havoc with the pipes and the holding tank! Ask me how I know. We did it in our TT we used to have, figured I could just wash the litter down the drain. Bad idea on my part. Now I vacuum the litter out of the tub/shower when the cat travels with us.
I just went out & measured the tub in our Jayflight. The basin is about 37" x 20" and about 12" deep. It's about 40" x 24" overall. Definitely not large but perhaps usable. We've never used it as a tub, just as a shower and it's pretty tight for me but then I'm 6'-5".
Hope this helps...
2008 Ford F250 Super Duty, Lariat, 6.4l PSD, Super Cab. Long Bed
2006 Jayco Jay Flight 27.5 RLS Fifth Wheel