Point-of-use tankless water heaters

Previous owner was an absolute goof so I doubt he serviced anything on there properly. I'm hoping the roof is okay because a buddy and I were walking around up there looking for leaks and soft spots and couldn't find any. You are absolutely correct in these projects being money pits. Can put lipstick on a pig but it's still a pig haha. Can I put any model of hot water heater in there or does it have to be specific to my trailer? I found the cheaper units you were talking about on Amazon about 300 bucks US. It's 650 without install from my local RV dealership so if it's cheaper then that to order online from the state's then I'll go down that route. When I first searched for these the price ranged from 8 to 12 so it's nice to see that's not what I'm stuck with.