i always have a right fanny on with insurance i recently got a quote and im gonna take it at the end of the month....its the new admiral multicar policy and it was much better than anything else i got....
for 1088 quid i got the g40 insured third party fire and theft in my own name with 3 points and no no claims bonus...my girlfriend also insured on it...AND....her 54 plate punto fully comp with both of us insured on that too...both with social domestic and pleasure and commuting....this works out about 400 ish for the punto and 600 ish for the g40...admitiddly not the cheapest but im 24 have never had my own insurance for the same reasons you mentioned and therfore have always been a named driver with my mother on the g40...so now im happy i can build my own up...
anyway i would give them a call if you have two to insure as it breaks down the individual cost of the cars and 600 and odd was way better than the 1300+ i was getting for the g40 on its own elsewhere...
one catch though..if you cant pay all up front which i cant at the moment..you get hammered on interest...monthly we will be paying 111 a month for the two...65 for the G40 (i currently pay 60 as a named driver with tesco etc) and 46 for the punto....
personally i think youll struggle at 18 years oldon a g40 but its not impossible...i dont think a g40 in the hands of a g40 is a good idea anyway...i think there is a high chance of crashing...i started on a cl and moved up...helps you learn how a basic car works without good breaks etc...just my opinion anyway...good luck