I had an early 90's Destiny at 700(ish)Kg and I also have a slope up to my garage. With my door I had 5cm clearance each side. The slope rises 10 inches in just over 3 feet, putting it at 1:4.
You may not be able to back it in even if you are good enough at reversing as it will ground with the hitch at tow ball height. It does depend on how steep the slope and how high the tow ball is. If the slope is not steep enough to ground and depending on the tow vehicle you could have a second detachable towball on the front. I have seen this on farmer's landrovers so they can unchitch the trailer, turn round and hitch up again at the front and see what they are doing as the push the trailer into a barn. Not really practical for regular cars though.
The solution I came up with was to buy a Stanley chain hoist that is rated 1000 Kg for a horizontal pull as well as for lifting. You can order them with varying lengths of chain. I bought one with a 5m lift. I think I paid £130 for it, which was quite a lot, but then the alternative was to pay to store my Dandy and that would have been twice as much per year. I bolted a couple of plates to the concrete floor at the back either side of the door centreline. Each one had some thick nylon rope with a loop at the end. The theory being that if one plate or rope failed there was a backup. The hook on the hoist block goes on both loops and live hook went to a second pair of loops that were tied to the A frame. I did not want the chain to be stressed on the edges of the frame. You can then stand in the garage and by pulling on the continuous chain loop slowly winch it in. the hoist has a huge mechanical advantage, so the actual pulling effort is low, but you do have to pull an awful lot of chain through. because you are in the garage and above the Dandy, it will not run you over if anything slips. you can also steer it with one hand while pulling chain through with the other hand. It moves so slowly that the 5cm clearance each side is not a problem.
There are a couple of sites I took the destiny to that did not allow cars on the filed and in case it rained, the hoist was a handy backup to help me drag the Destiny back to the car with a couple on 18 in 'tent pegs' to uses as a ground anchor.
I have since sold the Destiny and bought a much smaller 4/5. I still sometimes use the hoist even though with a run up I can just get the 4/5 in on my own. With a helper pushing as well no hoist is needed. Obviously the 4/5 has a lot more clearance so I am confident getting up some speed before hitting the ramp. With just 5cm each side on the Destiny, that was never an option.
Another tip may be to replace the jockey wheel. I did not do this with the Destiny, but did for the 4/5 and it makes hauling it about on grass much easier as well as smoothing out the bumps for my run up.
Remember about grounding as well. I had to get the front really low on the jockey wheel to prevent the back from grounding.
Hope this helps.