physical connections to a standby generator
Well just FYI, "rain tight" is false advertising.  Code requires you  to assume all exterior conduit is 100% full of water 100% of the time; the defense against wet is in the insulation.  

Code requires you fully assemble the conduit first, and then pull the wires through it.   I don't like pulling through flexible conduit; it fights too much.  So I'd either go Schedule 80 PVC or (if I had a pipe threader on site) IMC or Rigid.  The latter two can be used as the grounding path, so one less wire.  Sched 40 PVC is too fragile and easily cracked, especially after being sun-bleached. The sun is not kind to PVC pipe; paint it.  

Sched 80 has a smaller inside diameter (since the OD is the standard dimension for fittings), so you need to upsize the pipe sometimes.  You should upsize anyway if this is a DIY install, as it eases pulling - the last thing you want is get stuck on a pull and have to call an electrician merely for his truck full of pulling tools.

A bit for that reason, I would split it up, and have a conventional main panel straight off the meter, then a 100A transfer switch (the gen is only 70A anyway) to a 40-space subpanel.  Put most of the house circuits in the sub, and the non-generator-critical biggies in the main.  That way you're muscling around #1 aluminum (or #3 copper if it's short enough for the price not to matter) instead of #4/0 or #2/0.   The bigger reason is the main/transfer/sub will play well with emerging technologies like Tesla Powerwalls, EV chargers and solar. That stuff's price is just gonna keep falling.