The problem is the door hardware. It looks to me that the vertical bars need several inches of clearance to swing out.A yard of gravel solves your issues and isn't slippery.
For twice a year, kicking around some gravel isn't a big deal, maybe even use thin sandbags. For everyday riding I'd want something quick and easy. Never take the fun out of a ride by needing a mechano set to get the bike in and out.
If a shallow four-foot ditch would allow the doors to swing free, a removable four-foot ramp, six to eight feet wide would close the gap.
Would a pair of 40X48 skids do the job if the tops were filled?