I'm currently well into a large commission project, featuring 200 points of Tyranids. My client's army list features lots of mostrous creatures, and he wanted these pinned on Secret Weapon Miniatures resin bases. The Gieger-esque detail is very appropriate for Tyranids. The bases also paint up easily and nicely.
However, some of the GW larger beasts don't fix to the bases so easily. Both the Trygon and Flying Hive Tyrant have very small contact areas, meaning without some serious pinning the models simply wouldn't stay attached to the bases.
To solve this problem, I decided to pin the Trygons to the resin bases. This is easily done and should solve the issue.
First, I painted the model as usual - I also paint monstrous creatures in parts, and here I have painted up the tail section (as you can see, some cleaning up to be done to some parts). I then attached some heavy-gauge brass rod to the main tail section (3 rods) and the smaller tail end (1 rod).
You can hopefully just make out the rod pieces - like paper-clip wires but heavier...
The rods are about 1-1 1/2 cm long. I drilled long holes into the resin base (once it was painted), and then superglued the whole construction together.
Quick tip: I always paint red onto the pins once attached to the model, then whilst this is still wet "dry-fit" it to the base. The resulting red marks on the base provide a guide for the drill, in theory meaning everything will then fit comfortably together.
Here are two shots of the (almost finished) Trygon, now firmly attached to base. (Note there are still several areas to touch up, and obviously he has no head!)