I wired my 2nd transfer switch the way you are talking about doing. It's a continuous duty relay, as far as I know. I also agree that switching with the big loads that cause arcing, would be the problem making there. I also leave mine plugged in year round.
I used the transfer switch that just slides on the back of the WFCO converter, and it doesn't seem to be hot. The load on the coil only has to be strong enough to overcome the spring, regardless of load going through it. I agree, though that little parasitic loads like this don't belong on the batteries, so that was my thinking for wiring it that way.
