moving on from the quite irrelevant fibreglass topic. it looks like you have all the tools to be succesfull, germ your seeds in the paper towel, just like you're doing!! great.
get yourself some good bagged potting soil or top soil. if you are planning to use some sort of liquid fert/nute mix in your grow, dont get the bagged soil with fert added in. a very common problem stems from these pre ferted soil mixes. it is hard to tell when the plant has used up most of the available fert the soil came with. the newbie grower is watching the plant grow with anticipation, and convinces themselves its been two or three weeks, its time to start adding my nutes. nute burn occures, and the stress to the plant and the grower effects the grow from that point on. stay away from the pre ferted soils.
grab some perlite or vermiculite, and mix 3 parts soil to 1 part verm or perl. you dont need both, one or the other will do. the verm or perlite will promote good soil drainage and airation, both good things.
with that florencent tube in your pic, keep your seedlings under it for a good three weeks, at 18 hours on, 6 hours off, use a automatic timer, they are cheap and they work. two added bonuses to using the floro tube is its way cheaper to run than that 600watt hps, for the first three weeks, and the floro tube will provide the blue spectrum of light the plant requires in early life. the more blue spectrum promotes good veg growth, and you can place the floro light an inch or two away from the plants to keep them as short and bushy as possible. i honestly dont know why some people use only an HPS, it promotes a taller, spindlier weaker overall plant in the end, more often than not, that has to be supports and tied up so it doesnt fall over or break.
in 3 to 4 weeks, judge whether its time to put the plants under the 600watt HPS, and if you do, it would be wise to leave them at 18/6 for maybe 2 more weeks. then drop em down to 12/12.
cover the fiberglass insulation with mylar or, drywall painted white. if its an open space with some sort of fresh air supply, keep a few fans going to move the air and plants around, good air circulation is very important, how much circulation depends on the temps attained while the light is on. anywhere from 76 to as high as 84 degrees will be fine as long as the air is moving and there is a source of fresh air. try and keep the space from going below 60 degrees at night.
go for a humidty around 55% durring 90% of the grow, for the last three weeks i drop my humidity to 35-40%.
good luck