If you do go down the Brompton route by using the telescopic seat post you have another rolling option (on rack and easy wheels) as you can have the main seat post lowered (which locks the fold) then extend the upper part as handle to push the bike. This would work with the cover, I think. I made my own telescopic seat post which, having misjudged the shim size, didn't work out as cheaply as I hoped. . . but I chose a longer upper section which extends to a comfortable height for me to roll.