thelma65,
I live just outside Porthmadog and tow our twin axle Swift Conqueror regulary to the midlands.
I always use the same route. M54, A5 through Llangollen and Corwen, just past Corwen turn left to Bala, on entering Bala turn right onto A4212 signposted Porthmadog,after about 20 miles turn right at T-junction onto A470 then A487 to Porthmadog, at end of Porthmadog high street at traffic island turn left for Criccieth and Pwllheli, the Haven site is on the main road between Criccieth and Pwllheli.
A good easy tow, with excellent views. No problems along Porthmadog high street.
Make sure you abide by the speed limits, mobile speed checking vans, and have a good holiday.
Hamer.