Scotland West Coast

I might be able to but it will help if you say which part of the long west coast and which islands as there are many of them.

TinWheeler's advice will be excellent. If you're going in June, Midgie repellant and other measures
On visiting the islands, I'd add that when we went to the Western Isles we found it really helped to  have the ferry booked first. At least one site owner, before taking our booking, asked if we had that, to make sure we'd arrive.
As well as TW's advice, I recommend looking at the reviews on a site I couldn't name here last time I tried, as the machinery automatically changed the address, but it's the (abbreviation for) United Kingdom   Camp   sites (all one word) one! This helped no end.

If you're interested in visiting islands you'll need to check out the CalMac website this is Caledonian MacBrayne ferries. There have been a few service problems recently but booking ahead is the best way to organise a trip. CalMac have tour ideas on their web site. Also individual island tourist info will put you in the direction of camp sites etc. 

I think that you can no longer just turn up at one of the ferry terminals and expect to get onto a ferry, as one could once upon a time, your ferry crossing now needs to be booked in advance, be it only the day before.

If it's the Outer Hebrides you are thinking of I would suggest you have a look at the Andrew Ditton videos on YouTube. He has done several covering a range of topics. This is the first in the series https://www.youtube.com/watch?v=AnCY6cizghg&t=12s

David

Hi, we can recommend North Ledaig North of Oban. Bunree, South of Fort William. There are lots smaller sites and CLs over in Arisaig. We have stayed at Small Isles CL and can recommend it. Further North, Ardmair Point and Clachtoll are two of our favourites. All highly recommended and right on the water / beach. One day we might get to the Islands 🤞🙂

We are also touring the western isles but my daughter has rented a house on Harris for a family get together end of August for a week.  Our plan is to store the van for 9 nights on a site at Loch Lomond or thereabouts to avoid towing through Glen Coe. Then pick up the van and travel onward to Oban with a view to crossing to Northern Island and home to West Wales via Fishguard/Pembroke. Does anyone know if this is feasible? 

Can you clarify "Northern Island", please? Ferries from Oban sail to the Inner and Outer Hebrides. If you mean Northern Ireland, Oban isn’t the place to be.

There's no problem with towing a caravan along the A82 from Crianlarich through Glencoe and beyond. The stretch of that road most of us avoid is the section running alongside Loch Lomond.

I don’t know how long you plan to take for this trip but I reckon you’re packing an awful lot into one holiday.

I presume you mean Northern Ireland and the quick route is via Cairn Ryan from Dumfries and Galloway. Then drive south to Eire to pick up the Fishguard ferry. A lot of driving but do-able. 

Edit   ferries to Ireland are quite expensive.

Some good points have been made in posts already. 

Tinwheeler's first post is worth responding to as you may be able to receive further helpful ideas.

Other points to consider are:

What do you mean by "good sites"?  ie what do you require to consider a site to be good?

Have you done any initial research to identify exactly where you want to go? 

What do you want to do and see?

If not, I suggest that a visit to a library to borrow a guide book will help. Also, it will be worth looking at a road atlas to see where places and individual islands are.

It is also worth remembering that what one individual/couple likes may not suit someone else.

If you get back with further details then you may receive some suggestions that will help you.

Unfortunately, some initial requests  for holiday ideas are so vague with the persons never replying, even after suggestions are made, that one sometimes wonders if they are genuine.  Some enquirers do not have the courtesy to acknowledge  with a general thank you post that there have been responses to their request.   I'm not suggesting that you are like that but the more specific you can be will mean that responses can be more useful to you. Many people on this forum are glad to help. Hopefully, this will be the case here.