ralph, nice trailer! I know you must be excited.
Your question is dependent on a few things:
1. Will you be camping in cold weather a lot. A furnace really drinks a lot of propane.
2. If you have a gas & electric water heater and will be at campgrounds with electric, you will save a ton of gas using the electric.
If you will be at campgrounds with hookups and not a ton of cold weather camping I think you will be alright with the 20lb. tanks. If you will be boon docking a lot then you may want to consider the 30lb. bottles.
IMHO I would wait and see how it goes. Spend your money is some other areas to upgrade.
Have a blast!
Philip, DW, 3 DD, 1 DS, and Kadie our Dog
2013 Flagstaff V-Lite 30WTBS
2003 Ford Expedition 5.4 Liter with 3.73 Axle
Equalizer 4-Point Sway 12000# & Tekonsha P3
48 Days of Camping Reserved for 2012