I think you will be close enough to 1000 lbs TW (loaded) that using the 10k/1000 unit is a risk. Also, it would be nice to not have to upgrade the WDH should you decide to get something heavier in a few years.
I see no downside to you getting the 12k/1200 Equil-i-zer, besides a neglegible weight increase.
Most of us with ultralights have to chose between the 6,000 and 10,000 lbs units. Always better to err on the high side. My camper is rarely over 5,000 lbs loaded, and I'm very happy with my 10k Equil-i-zer.
thebrakeman ('70), DW ('71), DD ('99), DD ('01), DD ('05)
2004 Surveyor SV261T (UltraLite Bunkhouse Hybrid)
2006 Mercury Mountaineer V8 AWD Premier
Equal-i-zer WDH (10k), Prodigy Brake Controller