Yes you will need a WDH, and the Equal-i-zer brand is an excellent choice. You will likely add more than 60 lbs, as the LP tanks aren't only thing that add TW. Then again, you may have some rear storage that would offset what's put in the front.
But for a 21SS, the 10,000 lbs (1,000lb TW max) is the Equal-i-zer model you want. If they made an 800 lbs model, that might work. But they don't, so we all get the 1,000 lb unit for these hybrids. Works great for me.
For brake controller, "Prodigy" is a model that used to be made by Tekonsha. I have the original Prodigy, and it's still going strong, going into it's 11th camping season. The model currently available that is comparable is actually called the Tekonsha "P2" although some still call it the "Prodigy" or "Prodigy P2".
The Tekonsha "P3" can also be had. Will perform the same as the P2 for you, but has a more user-friendly user-interface. This might be labeled "P3" or erroneously "Prodigy P3".
Either of these are fantastic bang-for-your-buck controllers, and highly recommended on any camping site. There is also a Tekonsha Primus, but you aren't going to save much money there, and you'll lose some of the P2/P3 features.
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