3-D cakes - keep them standing!!

Need help again from those of you who are more advanced than I . . .

I'm doing a 3-D Thomas the Tank cake tonight.  I've done one before and delivered it myself so it got there standing up.  But the one that I'm delivering tomorrow is going to the grandparents and they are taking it to the party on Sunday. 

I'm very nervous that it won't stay standing.  What type of support would ya'll recommend???

THANKS!!!
Becca