For the TT at my seasonal site, I use my "good enough" level. In other words, I don't make my trailer perfectly level
because within my region, my trailer is sitting on soft soil. My deck and trailer "float around" - after each massive rain. But, I do try to get my TT pretty close to level, and re-level it every 2 months. Always checking the fridge floor level a few days after the massive rain storms. In reality, only its fridge needs to be near level.
Talk about level.... I noticed my TT's large slide flat roof is getting a natural sag. This sag allows water to collect in its middle. While storing my TT during its winter months, I now install an adjustable support post. With slide IN, I then install this post from floor to its main beam. And, I apply tension - to force an upward bow (in its main beam). In the spring (when post is removed), my slide's large flat roof is now flat.
Slide Roof (before): http://i178.photobucket.com/albums/w...e/100_0358.jpg
Adjustable suppot post (when slide is IN): http://2.imimg.com/data2/MK/PO/IMFCP...ps-500x500.jpg
Also... Put jacks or cement blocks on wide 18" or 24" wide thick padio stones. The wider the ground surface, the better. And, wider means it sinks less in the ground (especially during frost months).
Hope this helps at your seasonal site....