I would just use one crystal malt; either crystal 20 or crystal 40, maybe C-60L. Too much crystal malts in an IPA clash with the hops and are cloying IMHO. Not more than 5% of the grist.
If use stick with domestic 2-row I would use 5-10% Munich for the grist. It adds some nice malt complexity with biscuit, bread, toast, and melanoidin complexity. A little more assertive than MO. You will not get this with carapils. In all honesty, you probably don't need any carapils.
Remember, change one thing at a time.