I'm not a fan of flex drain tubing (aka "corrugated pipe"). It clogs with leaves and debris. Use schedule 20 or schedule 40 PVC, this way if need be it can snaked out. Now.... I realize you want this job. Realize you're hoping to get it and are excited about the prospect of getting it. The thicker base will not do an ounce of good, if there is a water issue. Nope. Think about this - if the dwelling's foundation is sinking........so will your wall. A dwelling has a much better foundation than even my walls have. First step - identify the water issue. After the water issue is overcome....then let's talk walls.