Car covers worth buying for outside start at about the cost of the car port you mention, a good quality one will last 10+ years, but that car port will be useful all year round.

Suggest you leave the windows open a crack so the interior can breath, or you can get mould growing if it's under a cover.

I left a new Varta battery on trickle charge over the winter on the car, being a CTEK smart charger it packed up unbeknown to me and the battery was scrap after the winter, so might be safer and easier to remove and just charge regularly during the winter.

Nothing wrong with a safe anti frost heater but it shouldn't be needed.

Don't know how the parking brake works on that car, could be drum inside disc on a Toyota which are prone rusting on even after washing and parking for a few days, so make sure you park it up with dry (short run if you wash it before storing) brake discs/drums, and leave the parking brake off if at possible, also worth starting every couple of months and make sure the clutch isn't rusting onto the plate be engaging drive for a few seconds, that has been known to be an issue on parked cars in times gone by.

Last thing, make sure coolant anti freeze is up to strength.

Last year I bought it a cover, a rain proof breathable one. When I checked under the cover during a cold spell it was frozen to the car. I am now looking for another, yet reluctant to spend a lot on one as I can build a car port for a couple of hundred pounds.

Do that then.

Seems fairly obvious that's a better use of your money.

My 'daily' car has spent its life in the open, and I am lucky enough to keep my occasional car indoors, so I have no personal advice to offer here. Costs being equal, I would suggest that a rigid structure would be better than a car-cover simply because of the breathing space around the car. Car covers are a last resort - their only saving grace is they can be folded away in summer. Also you can easily see what is happening under a carport ....