Various editoins of the Monmouthshire Merlin, 23rd April 1831 report the death at her house in the Burrowes, Swansea, of Mrs. Martha Mansel, the relict of Rawleigh Dawkin Mansel, in her 85th year.
In March 1891 the Cardiff Times published an item on the Parliamentary History of Pembroke, listing MPs. I realise the dates are wrong for your Rawleigh, but working on the assumption names run in such families this may give a clue? Unfortunately I can;t locate Abercover
1722, December. William Owen, vice General Ferrers, deceased. He has be6n previously treated of as member for the county, 1747-61. Re-elected for the borough 1727, 1734-, 1741 (when
Rawleigh Mansel, of Abercover, Carmarthenshire, presented a. petition, which the House dismissed February, 1742), and 1747. He was Lord-Lieutenant of Pembrokeshire and of the liberty of Haverfordwest.
Perhaps this will amuse - some one was researching this line in 1892!
http://newspapers.library.wales/view/3339380/3339388/94/rawleigh