That sounds like a pretty good plan - though all the wrapping may look a bit chunky near the end. If you do paint the tub, make sure that you rough the plastic up really good first with sandpaper, then wash it out & get rid of all oily residues on it (rinse out any mild soap you may use really well). Then, use a good primer on the plastic, and finish off with a marine paint (waterproof). You may want to put some sort of 'texture' on the bottom to make it a bit less slippery.

I've been idly playing with an idea of how to make a wood-fire-heated portable hot tub, and I had more or less used the 300-gallon tank starter idea in my plans. From there, I'd have the outlet from the tub near the bottom (actually, ideally at the bottom of a side if the tank were resting on the ground, or actually at the center bottom, if it were somehow elevated about 6 inches or so). Anyway, metal piping would then lead (sloping slightly down) to a mini wood stove with a copper (or other metal) piping coil, sloping upwards in the coil. The piping would come out the top of the stove, and then would head back to the tank.

The main concerns with this setup would be strengthening and insulating the places where the piping meets the tank and having the stove slightly lower than the tank. An option is also to put a pump on the outlet side, pumping into the heater, run off a deep-cycle battery (possibly recharged a bit via solar during the day) - though I had been curious how much circulation could be done simply by cold water sinking, hot rising, and bodies mixing the water in the tub.

The idea is a semi-temporary set-up for extended camping trips - with the water supplied by lakes/rivers/etc...