I play both Tau and Podding Marines, and have done so for ever. I'm building the Skyhammer Formation, and intend to use it in a large tournament in July, backed up by lots (and lots) of bikes.
As a Tau player, Im not convinced bubble wrap and castling is the way to defeat this formation
With the greatest of respect, I feel people are overestimating the power of EWO. There are many people far better at maths on ATT than I, but a unit of intercepting broadsides will kill maybe 3 marines (assuming they are part of the fire base cadre)? One could counter this by combat squading the dev squad, putting 2 grav cannons in each squad, and putting the bolter marines at the front, taking them off first, and then opening up with the grav cannons (assuming of course you pass your leadership test... but they're L8). Plasma rifles are perhaps more worrying, but not really. It should be reasonably straightforward to deep strike your marines into terrain for a cover save (contrary to what was said earlier in the thread, this is perfectly legal - you simply need to ask a dangerous terrain test). If there is no terrain, then the Tau player's bubble wrap will probably give you a cover save!
As for Riptides, their large blast can be countered with only a reasonable amount of luck. You simply deepstrike your pods as close to your opponent as possible (remember you can't mishap unless you go off the board) and deploy your dev 1" away from your opponents models. In that way the blast marker can not be placed, as it will overlap your own models. Harder to do with the assault squads, but I would be tempted to go for risky deepstrikes, other wise what's the point of the formation? Mishaps are much more forgiving now. And let's not forget, Riptides are only BS3.
And for all of them, it would be reasonably straightforward to put a character in front with a 2+/3++ to tank all the interceptor fire.
As for bubble wrap, that can be effective, but grav cannons have a 24" range so can reach "over" all but the most extensive bubble wrap.
But I think the biggest problem with castling is that you give up board control. Because you put all your heavy hitters on the board, to try and kill the alpha strike, and then wrap them in kroot, and then you opponent wraps them in marines, it's hard to then "breakout" of the castle. While you're locked in your castle dealing with the alpha strike, your opponent is running around the board taking maelstrom objectives and winning the game.
No, I'm afraid IMHO castling with kroot bubble wrap, is not the way to defeat this formation as a Tau player.