Don't get all wrapped up in the must have 100% charge every day. The solar kit is fine and will serve you well. 120 watts is plenty to charge one to four batteries just fine. If your camping usage exceeds the solar production your charge level just drifts down a bit each day. Then at the end of the trip the solar will catch up and charge the battery to 100%. Plenty of RV batteries operate every day and don't ever get 14.8 volts as converters don't go that high.
Yes performance will improve with some #10 wire and the controller mounted close to the battery. Go ahead and mount the panel on the roof and let the solar start working every day.
Get out camping a few times to evaluate performance for your needs. Go at least once with the existing battery... it might just work out fine.
No fancy battery monitor needed IMO. LED light should be first.
