the diameter size depends on what your trailer already has, unless you want to try drilling it out to make it bigger.
seeing that it's a popup, should be the 2" diameter.
any electric tongue jack will do, since they are all over-spec'd for the actual tongue weights.
check Ebay for remanufactured ones under $100.
and Zoe the Wonder Dog(R.I.P.)
'07 Roo 23SS pushing an '07 Chevy Avalanche
Equalizer WDH and Prodigy BC