With the mast base on the trampoline and relatively close to the mast step on the front beam...have the mast pointing rearward extending out over the rear beam of the boat. Attach both shrouds and leave the forestay loose. Step the mast (it's easier if someone can walk it up to you while you stand on the trampoline). Most trailers should be attached to a car so it doesn't pop a wheelie with all you and the mast weight behind the axle. Step the mast and push against the connected shrouds while the buddy that helped walk the mast up to you connects the forestay.

You don't want to step the mast with nothing connected - it will be practically impossible to control and keep standing.

Now, that said, I am not intimately familiar with the Isotope and some cats are stepped a little differently.