I did end up buying 2 of the Shallco relays. I was concerned about the dissipation of MOSFETS in a high amperage solution, too. Let’s not forget that all that heat is also wasted energy as well. So I have 1 to use and 1 as a spare part for the future, not that I expect to ever need it. The relay is rated for 100,000 cycles, and everything going well, it should never need to activate.
Now if I could just get some Attinys I’d finally be able to get my BMS up!