windshield gasket for 1999 Holiday Rambler

I think your housing is fiberglass and won't be rusted out.
Take your rig to an auto glass shop.
Several years ago I took our 96 Southwind to a glass shop because of a small leak around the windshield, it looked like the windshield was loose.
They said the factory did not use enough sealant around the windshield gasket when it was built. They removed, cleaned and reset both windshields using enough sealant with the original gasket.
It has not leaked since the windshields were reset.
An auto glass shop that works on motor homes will know what they're doing.

Check to see if it is just a loose dash which is making the windshield appear loose. The front cap should be fiberglass and maybe the steel supports have come loose or there are broken welds.

auto glass shop, some they can make. but loose? sounds like you might have a rusted out housing.