I'd be more worried about coming down a hill than getting stuck going up one (although being dragged backwards after getting stuck is a jump off and run scenario)
Our little quad is a nightmare coming down a hill with lots of weight on the back - you have to be committed as stopping is not an option. Corners are dangerous as the load is heavier than the pulling vehicle and unless your excellerating - the load is pushing.
I have a ride on lawnmower - gone rusty and never used - the thing cant even ride up a tiny bank with me sat on it - bleeding useless.
Still though - if I had an old ride on mower - it would have to be converted into something useful or it would go on eBay
I would have thought that you could get a 20 liter drum on the front and back and travel on a flat no probs.