I like almost all of Giant Leap's products, but not this one. Our club got that tower and it is really flexible, on top of being heavy, large and hard to transport.
I made a cheap, transportable and stiff tower with the following from Home Depot:
3 shower rods, 1" aluminmum, $5 each
2' x 2' piece of 3/4" plywood $5-$10
3 1/4" lag screws
About a dozen 1/4" T-nuts
18" x 18" galvanized sheet steel
15-minute epoxy
The basic idea is to glue the lag screws into the ends of the shower rods, glue down the sheet steel on top of the plywood, and then screw the rods onto the base using the T-nuts on the back side of the plywood. Why this works is that the shower rods are straight and pretty large diameter, so they're reasonably rigid on their own. The bolts preload them onto the base, and the sheet steel on top of the plywood makes a good metal-metal contact with the ends of the tube, so you can screw them into the base pretty hard. You can make several different hole patterns for different sized rockets. If you work out the math, rods tubes a little over an inch are the largest that can still work with a 13mm tube.
Stabilizing the tube ends at the top is optional, but recommended. I made an elaborate adjustable ring holder to keep the tube ends in just the right spot, but then forgot it when I went to the field the first time. I cut out a cardboard stabilizer and used 24mm coupler sections to fit into the ends of the tube, and it worked quite well to keep the tube ends all in the right spot. I'll post some pictures next.