Trampoline training is as fun and challenging as wakeboarding.....but BE SAFE.
As for a tramp...try to find a used gymnastics quality rectangular one... Look for an old Nissin...the original heavy duty design that is still used by Eurotramp...
I would also recommend you find a competitive gymnastics/trampoline gym and get some basic coaching. Learn the basic gymnastics moves. The control that this gives you WILL save you from serious injury. It has saved me...I know that for certain.
Just because you can hop on the trampoline and learn/do a flip quickly...does not mean you should. What is going to happen when you are learning spinning flips...and you under or over rotate? You are not going to know how to manipulate your body in the air to save yourself....and you will get hurt. Front rotations with full spins...and back rotations with 1/2 spins are especially dangerous if you over-rotate and do not know how to land. Contrary to popular belief...many serious injuries on the trampoline (ie broken necks) occur when you land ON the trampoline head first...pile driver style...not just when you fly off and hit the ground.
Learn all this before you start doing really big flips....and especially before starting spinning flips...
3/4 front to back (crash dive...THE single most important move to have to save your neck!)
3/4 back to stomach
Learn all these moves..and be able to link them up to each other. This will also teach you amazing body control that will dramatically improve your ability to manipulate your body in the air while wakeboarding... And when you are learning a new move on the tramp...and you mess up...you will know where you are...and you will know how to control your body at the last instant to protect yourself from injury.
Back with 180 out
Front tuck or pike with very early kickout....
Barani (Front with mid to late 180)
The building block skills that will lead to the biggest break throughs in flipping with twists are the back straight, barani (front flip with mid 180...both straight and tucked) and the arabian (Starts like a back straight...with very early 180 twist...then becomes a front flip) Once you have these moves....your flipping skills with twists will build fast...
It is true that gymnastics form is quite a bit different that wakeboarding form...but the body control in the air is what you are learning.
As an aside...trampoline skills are very much like wakeboard skills in the way that simple skills build upon each other in a progression to get to very complex moves...
I started jumping about 8 months ago...and I could do NOTHING. I am up to the barani and back out, and working on the arabian. I have landed doubles both front and back...but that was in the belt (=courage). Interestingly...the skill that scared me the most...was doing to simple back pullover to stomach. I did a number of pile drivers learning that.... that and flying off the trampoline a few times trying to do a barani with the spin opposite my natural rotation direction... thank god I knew how to do a crash dive...or I might be eating through a tube...