Richard Fenton was a classic antiquarian country gent who loved to take a spade to the middle of a barrow or two. There are some great early 19th century accounts in Archaeologia Cambrensis of him and the society having tea parties at ancient sites, except that the desert would be to uncover an urn or two (of course throwing away all the cremated remains). His book 'A Historical Tour Through Pembrokeshire' (1810) probably has an account of his visit.

Some of the Scottish sites that are kinda similar to this are the Bargrennan tombs. One, near Glentrool just north of Newton Stewart, was investigated last year and is to be resumed later this summer. It is called Cairnderry, and has three large chambers, each with a passage leading to out from the centre, and a mound or cairn probably covered the whole thing. It is kinda egg-shaped. The interim report can be found at:
www.cf.ac.uk/hisar/people/vc/cdy/cairnderry.html

the other tombs are listed on:
http://www.megalithic.co.uk/article.php?sid=5390

Again, it was robbed out by antiquarians and many of the stones were used in the construction of an estate wall sometime last century. Its still quite interesting though.