Tom, In a
Trillium 4500, there are eight bolts. Two each in the rear dinette seats and though I have never personally seen a front dinette
Trillium, or almost dinette, (that is what you should have) there should be two bolts in each of the front dinette seats. They will have a large square washer.
Typically these are rusted right through, or nearly so. You will need someone in the trailer to hold the head of the bolt with a pair of vice grips, and someone underneath with a big wrench, (or impact). The frame bolts are one of five maintenance items on an old Trillium.
The others are:
Wood in the window frames
Re-hang door
Belly band repair
Replace
axle, (you are already on this one)