I just ordered Intellipower 9200 models from Vintage Trailer Supply. Good price last week.
You'll also need a fuse block of some kind, if your Sovereign
doesn't have one separate from the Univolt. Sometimes you can remove the fuse block that's in the Univolt and mount it on standoffs. Otherwise, fuse blocks are $17-35. I recommend that if you do get a new fuse block, get one that uses the standard size automotive fuses. These come in sizes from 3-40 amps. I haven't found a need for anything more than 40. Some members will say you need 60 amps for the batteries, which might be theoretically true, but not in practice, unless to totally flatten a battery (bad, bad practice. always leave at least 20% charge on a lead-acid battery).
If your new fuse block uses automotive fuses, you don't need a battery switch--just pull the appropriate fuse(s). That'll save you $20 right there.
Also, I don't fuse both leads from the battery, just the positive lead. There are some remotely possible failures (battery + lead insulation breaking down and shorting to the shell) that a negative lead fuse will protect you from, but they are so improbable that in my judgment the second fuse is a total waste.