As someone who has stepped off one of those things as it started to tip and watched it roll/bounce it's way down the hill, I agree with the comment to be careful with your centre of gravity. Your concerns regarding steering when the front is heavily loaded is also justified. That said I think your biggest issue is going to be traction - it isn't hard to get all 4 spinning (I presume it is 4wd) when towing heavy loads (once it has traction, it will pull your house truck). Putting the weight over the wheels will help but then you are back to your heavy steering issue. I'm sure with your skills you will come up with something to amaze us all just like your other projects.