Are you seriously considering pulling a 30' boat with a Rav4?
4WD turbo, good torque. why not? but the drive terrain is the only issue i see with this whole project.
Pulling a 95 EX with a v6 Ranger was bad enough. Even a 26' boat on a F-250 has issues. I agree, drivetrain will be the issue. An AWD version will overstress the transfer case, and a FWD version will get no traction. Trust me, I've seen some tools use minivans for the wrong application before. That's all assuming the enigine doesn't melt - occational boost is one thing, cruising at 5psi is another story (with a bad ending).
Back to the turbo - why not get the competing model to the Rav4, the CR-V? You have a decent motor, the trans can take some abuse, and boosting it will not be difficult. Worst-case you can convert it to a normal B-series FWD setup with some work.
Overall, I rate you idea with a D-. Nothing with a turbo can really get an F, fyi.