Whichever way you go, make sure you season your RTT (or any canvas goods for that matter) before heading off and finding out it leaks.
Soggy sleeping gear isn't much fun in the snow.
"Season" means setting it up and giving it a thorough squirt, maybe with a garden hose.
Make sure you hit all the seams and zips.
Do it a couple of times.
Most fresh canvas needs to get wet to swell up and seal joins/stitching etc.
When you're happy it's water tight, let it dry out thoroughly before pack down else you'll have a mouldy mess to sleep in next time.
I've seen quite a few of the Adventure Kings RTTs in the field.
Not too bad for the money, but I have other things to load on my roof rack so it's not an option for me.
I'm a "swag-on-a-stretcher" kinda bloke.