Ok.. The "pad" question... I have 1/2" rebar plus wire in the slab. It cracked.. Of course, but is not coming apart...
Run plastic "electrical conduit" of about 2-1/2" diameter under the slab. Cap off. If I "need" it.. It is already there!
Slab must be level.. To a 1/8" drop per 5-10 feet... So that waster runs off without "pooling". Also have a "broom" finish so there are no "slips"... Run broom in direction of slope for water shedding.
If rain runoff likely, create curb on sides of slab high enough to deal with anticipated volume. Also dig more of a "footer" on those sides to minimize "undercut".
If able to place a gate on the approach, instal a vertical pipe(s) for gate pins socket. That way you can pin the gate closed. Add other pins in proper arc so you can latch open and wind won't slam gate into trailer as you pull out.
Put in "stop block" where rear tires always stop. If you have a dedicated location. On mine there are several locations I can park, so this is a moot point...
If you can install a "cover", put weld plates in the slab where you can attach at a later time. Or you can install one near the tongue where you can secure AS with a chain.
Round smooth the edges...a couple of stubbed toes will explain why...
Peace and Blessings..