Okay - made some good progress on this during the afternoon. I like the way that the spider with howdah/bolt thrower turned out. I also based one of the spiders in preperation of rigging a saddle or some such on it. Here are some more pictures:
Same two angles as before:


Here is the pair mounted on the bases - custom sized 60X20mm from some leftover movement tray pieces.

Here is a High Elf Hero and entourage bravely preparing to engage a monster spider...

Unfortunately they do not see the danger lurking behind them...

I like that scurry movement idea...maybe it's allowed at a -1 Command instead of once per game...that might make it too fast.