Thanks to both of you for your advice--but I think I might have
stumbled upon a solution.

Went to Lowe's to get another box of fuses--have been getting Buss 20
amp, time delay fuses--they didn't have any with a base that matched
mine. Then I noticed there was a cubbyhole that had fuses that looked
identical to the ones I have been using--same color, size, base. Only
these were labeled "heavy duty," and the innards looked slightly
different from the ones I'd been using.

I bought them instead, plugged them in yesterday, and so far, no
problems--I even bumped down the thermostat, and they've been able to
handle the load. I suspect that, last year, I might have bought the
wrong type fuses for that circuit, 20 amp fuses that looked exactly the
same as the old fuses, even said on the box they were meant for things
like AC's, etc. This year, when an old one got blown, I started
replacing them w/the new batch, and that's when the problems began...?
Seems like a valid theory, at least. I'll give it a week. (crosses
fingers)

Thanks again for your help--I might still look into that hard start
device if it starts getting cranky again.

Cheers,
David