Leveling confusion

I have read all the posts I could find on leveling the TM. The dealer just told me to use 2x4's under the wheels. The manual (for 2007 model 2619) says to first level front to back with you tongue jacks (placing a bubble on your refrigerator) then to use your scissor jack for the side leveling for your low side.

So where do the 2x4's come in? Also, aren't you supposed to try and level it before you open it, so it will open properly? Are you supposed to slide 2x4's under the tires after you lift low side with scissor jack or do you just leave the scissor jack up to keep it level. Very confusing when you are new to all of this. Someone else posed my same question in a previous post, but no one addressed the question. I saw these on Amazon:

http://www.amazon.com/gp/product/B00...luc_bxgy_01_01

Looked kind of cool and only 8 lbs and compact. (Tri Linnx Levelers) Instead of lugging 2x4's around.

Second question: If you change your 14" tires to 15" tires and install a lift kit, will you still have enough length in your scissor jacks after your trailer gets lifted up to utilize them properly?