what area are you located in goat?

Leave fuel tanks topped up and use a water separating filter and you shouldn’t  have issues with  condensation in the tank. 

Turn the batteries off when you park it up. 

Cover over the top is ideal but you want it to fit fairly snug and not flap in the wind. 

Nose down is bad if you get water on the deck. I jack mine up at the front and put an axle stand underneath. Leave the bungs out so any rain that does get in flows straight out. Also makes it less attractive to thieves when the draw bar is up high and they can’t just hook up. 

 Storing the boat outside it will always find a way to let the water in. Find or make a wood block that fits under the jockey wheel when fully up and place that under before winding up to disconnect from the car and then you get some extra height from the jockey wheel end. You don't want water to settle inside the boat.

Fibreglass is used to make all of those gin palaces you see in the Marinas so you can expect it will hold up against the ellements. Regular washing, polishing and waxing will keep the shine.

As for security, make everything removable and never store anything on the boat that can be removed. If they get something once you can rest assured they will be back over and over again. I had 40 year old empty fire extinguishers taken during my rebuild so they aren't fussy or smart. No issues since putting up cctv and sensor lights though.

As for the fuel, use the boat as often as possible! Well, that's my theory anyway.

 You don't want water running forward and sitting there. If it is a Reefrunner, or really any boat with a lock-up cuddy, when the water on the forward-sloping deck gets high enough it will run over the step and into the cuddy. With most boats, thats as far as it will go, the footwell will be sealed , but you will then get condensation in there when it warms up. You reallly don't want that, the beauty of a good cuddy with a door is how you can keep everything absolutely dry in there. Water under the deck left sitting is not really desirable either, even with a boat with no wood under there or in the deck. My boat sits very level on the trailer, and ithe driveway slopes up slightly to the road,  but it took me a while to realise that I needed to have the jockey wheel on a brick and fully extended to make sure of all the wash-down water running out, and not just running forward. 

If you can't go with a good carport, a cover will certainly help. If it is a new boat, good washdown and an annual wax will keep it looking like new for a long time. Make sure nothing is hard-wired to the battery, make sure it all runs through the battery switches, and batteries shouldn't be an issue. And, as z00m says, use them as much as possible, for both yours' and the boats' sake!

Stabil is  a fuel stabiliser. 

Also a small trickle solar panel to keep to starter battery charged up.

 Some councils are really really hard nosed about this 

Thanks guys! Good tips as always!