I used a thick piece of wood that we cut down along the
long edges and stapled velcro to it to help with climbing
onto it (like a ramp) I then fill the tank to the level of the velcro to also assist him with getting up there. The actual
resting area is wide enough for him to spread out.

To secure this heavy wood, I used metal wreath like holders
two on each end that affix to the wood and then run up and over
the edge of the aquarium. So far it is the best thing I have
come up with. It's actually kinda funny that petstores sell
these crappy little basking areas. I got a deer in the
headlights look from one salesperson when she showed me what
types of basking areas were available and when I told her
how much my turtles weigh she didn't have any suggestions.
I guess they figure turtles never grow up!

Good luck
Linda