Hi Andy, nice to see you on this site, with ref to bubble wrap in your greenhouse, keep it on untill middle of april whem the tempreture is around 60f as this is the temp seeds germinate at, some people who use there greenhouse more than i do say keep, it on as it helps shade the plant of the sun, do you have any heat and water in your greenhouse, what sort of seeds or plant do you want to grow, do you wish to use the greenhouse all year round, as these things must be taken in to account , there are people with more knowlege about growing in greenhouses on this site that will give more advice
hope this helps
catch you later
windy :) :)