On my Compact jr. the pipe under the trailer is 1/2" (NPT) National Pipe Thread. My trailer has a hose with 1/2 female NPT on one end and the other end fits the regulator. I was in Lowes Sat. looking at gas fittings and they should have what you need. The gas fittings were in the heating department at that lowes with the winter gas heaters not the plumbing section.
Take your hose to Lowes or your local gas supplier and they should have the fitting you need. Also use pipe dope or teflon tape for gas and check for leaks
on all the fittings after you are done.