I may need a new compressor and I may have access to mighty vac a few weeks later, so I figured if I put the cover on now I'll have a couple months to blow the lines. It shouldn't be a big deal to lift cover when blowing returns.
As for main drain -
Does jandy valve really keep main drain air tight?
I'm not sure how important to have it blown when pool water is 1-3" below skimmer (in-ground pool), but with 33gal compressor only the closer md bubbles, mighty vac does a lot better job