To complete survival mode I suggest that you use as long of a trail as you can make, allow for a bunch(25+) teleport towers, and try to make as many surface to air missiles towers as you can. If you spread the TP towers out say 3 spaces apart starting mid way through your trail, you will find that the enemy will have a hard time getting back to the first TP tower. It takes a lot of money to keep the TP towers armed but by using this strategy it can done once you have leveled all your tower attributes up to about level 28. You will need at least 7-9 TP towers just for aircraft!! Be sure you unlock all of the locked add-ons before you make this attempt. Good luck!!
Once you finish any map in "Survival Mode"(an extremely difficult proposition, the levels jump up quickly and to finish you have to complete level 1000-100!!!) you will unlock a new game mode which allows you to randomly alter the attributes of your towers. Here is a list of a few useful numbers:
01000- long range missile towers 01275- long range gun towers 01205- very strong but expensive missile towers 01234- cheap missile towers