Hmmm yes dryhopping an IPA is very traditional. since they were made from only pale malt it is easy to make them from extract (incl the extract in kits)
These ales were shipped to India, America, Oz and even kiwiland in sailing ships. This means those beers were heavily hopped (and even so a lot of IPA was only fit for pouring into the harbor when it arrived at its destination port)
A trad IPA has an OG 1060 to 1080, the better ones started at OG 1070. So, work out the extract needed to reach that OG. use the palest extract, Muntons extralight. Now hop it right up, 100-150g of pellet hops (traditionally Goldings, some cascade will give it a lovely nose) boiled for 60-90 minutes.
That beer will be real bitter. Rack off the yeast cake after seven days (a keeping beer is racked off the yeast ASAP) Rack into a secondary fermenter, filling it right up with the least amount of headspace, adding half a cup of white cane sugar and 90g of dryhops. A keg that can be purged of oxygen is excellent. Now keep the yeast active by shaking/rocking the secondary, keeping the ale in the secondary a few weeks. Bottle and lightly prime. After six months the excessive bitterness is likely starting to mellow and turn into falvinoids. yup a long time to wait but oh so luscious a reard at the end!
I boiled my IPA for 3 hours with 410g whole goldings back in Oct. it will be racked off the dryhops (90g whole goldings) and bottled in July, and the first bottle cracked open at Christmass! By which time there will be some other kegs with long term maturing beers in them in my cellar.
You can do it!
Jovial Monk