New AC leaking and dirty inside

YES I would be concerned.....
New A/C Unit should not be dirty inside the Evap Coil area or Room Fan discharge plenum unless the 'installers' were careless and damaged plenum/sidewalls during install

A/C Unit sucks room air in...cools it and discharges back into room
NO outside air connection
Is the Return Air Filter Dirty??

As for all that water...evap coil can drip condensation
That should go into drip pan under the evap coil and have drain holes that allow the condensation to drain off and run away from A/C Unit....drip off of roof at whichever corner of rig is lowest

Sounds like drip pane drain holes are blocked and condensation is NOT draining out'
Could be Debris from the dirty installers
Could be the 'installers' tightened the hold down bolts TOO much crushing the roof gasket and A/C Pan is too close to roof so drip pan drain holes are blocked

New gasket should have been used
New gasket is 1" thick and hold down bolts should only be tighten enough to compress New gasket by 1/2
Hold down bolts should only be SNUG

New gasket was used correct.....old one would have been crushed already

Way too many RED Flags with the installation!

sounds like they installed a used unit on your rv. and didn,t even do a couple hour test run.

Take it back. Tell them to do it right, and test it before you pick it up.

Used unit and possible dishonest/lousy installer. Not a great combo.

Sounds like you got taken. Sorry to hear. Go back and demand a full refund. No point getting it done by the same dishonest place. Or better yet, go to a different place, explain the situation and ask if they'll take a look and give their opinion to back you up when you go for the refund.