I have the opposite problem - steep slope down to the garage, then the garage floor sloping towards the door to presumably loose any water ingress. The tail end of my trailer chassis is 0.25" above the floor as the wheel hits the drain at the door and the hitch on the car. At the top, the [pavem,ent also slopes the opposite way to the driveway, so I have a "peak" to get it over.
Bottom line is these things are designed for cars, which should mean that grounding probably
won't be an issue - I had to put 10" road wheels on my trailer to allow the frame through the garage door. Closely followed by having to move the spare wheel (which had been fitted exactly halfwaty between hitch & axle) to stop it grounding every time, and moving the midle rollers outboard (located exaxly in line with the spare!) so they could go up a bit & reduce the "drop" below the chassis. Having moved the guibbins, I have plenty of clearance on that hump - even with the smaller dia road wheels.
Your biggest problem might be smacking the top of the A- frame off the car port roof inches before the trailer wheels go over the "hump".......
Regarding keeping the brakes off if they are properly adjusted as long as you don't "shunt" the hitch (e.g bouncing over your non-existant kerb) they should reverse up the hill OK. If you find something that triggers the brakes, (the kerb is a good example) the trick is to attack it at speed to give the trailer a bit of momentum and let the trailer get itself over the bump / hole.