You can easily replace most incandescent 12v bulbs with one of lower output. Take a bulb out, get number on base, check on the specs of that bulb, and find another one (same base) with lower wattage and lumens!! Or as others have said, go to led bulbs, but there you will have to research output and find ones that are lower. Cheaper just to go to lower output incandescent bulbs, and they will take less power!!
Wedge base bulbs, 921 is very common in your year trailer:
# hrs/life lumens watts/amps color/kelvin
904 5,000 50.24 9.3/.689 2800-3000
906 1,000 75.36 9.3/.689 2800-3000
912 1,000 150.72 12.8/1.000 2800-3000
916 10,000 25.12 7.3/.541 2800-3000
917 1,200 126 15.4/1.200 2800-3000
918 500 81.64 7.2/.563 2800-3000
920 1,200 126 15.4/1.200 2800-3000
921 1,000 263.76 18/1.41 2800-3000 **** most common!! ****
922 200 188.4 12.5/.877
923 500 151 6 11.6/.906
If you have 921s, you can use 912 or 920 and cut light output by half.
If you don't have wedge base and have bayonet bulbs like 1003, you can do the same. Just look up the specs for the bulb you have!!!