As a matter of princip[le i hate agreeing with Richard B but those are good places in Lymington Port Solent is kwite a schlapp from Lymington, maybe a 100 mile round trip and the superstore is OK but it's not particularly powerboat focussed. You might find it's worth checking out BHG marines shop which I think is in Lymington or Bucklers Hard. Theres also a couple of good power boat places in Poole.
if yoiu do decide to drive to Porto Sol Ento however it's only a mile away from the motorway and is easy to find.
Heres a link to BHG website which isn't very sexy but it has the address
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