Ooh oooh! I know this one! I was in exactly your shoes several years ago. Lost two successive sets of seedlings before I figured out the solution. Since then I have had ZERO problem.
Start your seedlings on a table(s). I use a card table, anything would do.
Rodentproof the table legs by taking pie tins, or anything else like that, and cutting a hole through the center so you can run them up the table legs to a height of at least 2.5' and tape them there securely. I used plastic ice-cream tub lids, about 10" diameter, but there are any number of things that'd work. The key thing is that they need to be taped VERY SECURELY to the table legs, so they can't tilt over and don't have gaps around the leg where a mouse could squeeze through.
Rig the lights so they either rest on the card table (a bit wibbly tho), or hang from a ceiling that does not have mouse access (i.e.
not an exposed unfinished basement ceiling where mice can go across wires and plumbing to climb down the light chain and hop onto your plant table).
(e.t.a. - mouseproof the light cords similarly. I just ran mine up along one table leg where they could be protected by that leg's guard; but if you have ceiling-hung lights you might have to add an additional baffle on the cord itself)
Presto. No mice on plant table
Good luck, have fun,
Pat
Perhaps it can be modified with holes and screens added.
I'm going to be starting seeds soon...
Unless I find some silkie pullet chicks I can use those!
