Wow lots of noise from the naysayers. I have been carrying a 14' Portabote beneath my RV for about 7 years now without an issue. I just leave the bote beneath the trailer 24/7. If I am going to a destination with water I pull it out.
If water is unavailable the bote just stays put into the next time.
I have a wheel kit that I use to transport the Bote to the water from the camp site. With the wheel kit I can tow the bote behind my truck short distances on the CG roads. I can also just pull the bote to the river bank and launch is from the shore. No ramp required.
I carry the seats and etc. in a large duffle bag. I carry my 8.0hp Nissan motor in the basement of the fiver.
My current RV is a 5'er but I also carried the bote beneath my prior TT as well.
I have carried the bote on top of my old Ford Excursion SUV. This method is fine however I had to load and unload the bote each trip. When I got home. By carrying the bote beneath the RV. I have a lot less loading and unloading to do.
Pros of carrying bote beneath. Bote is always with you. Bote is out of the way and can stay underneath if you don't use it. Bote is out of site and does not attract attention.
Cons: Crawling around beneath the trailer is not fun. You must lay on your back to get bote in and out. I have improved my methods however its still not fun! If ground is wet,muddy or rocky laying on your back is a hassle.
TO the OP carrying beneath is very feasible however do not strap bote above axles. Strap bote in area clear of axles. Axles move up and down independently and may damage bote or make it harder to secure bote.
I secure my Bote beneath with ratchet straps.
Pota Bote link for those unfamiliar with the Bote! Photos below: First 2 are with fiver others are with TT
