Safe to assume sills full of sand was not in the Ford options list !  ............   it's dry sand and loose and easy to vacuum out at the inspection holes on the inside just a little above at floor level. As much as I try with flexible hoses on the vacuum cleaner pickup, I cant get it all out. Before I do the wrong thing like flushing out with water and maybe cause rust which is not there, I'd ask here to see if any one has a better idea?
I figured if the sand got in over the years via "gaps" in the metal joins, flushing may be the best way and maybe follow up with a hair dryer and then fish oil when all dry ???
 Car was in storage for 25 years before I purchased her several years ago which may be why she has very little rust.
This all started when I purchased new Crash Pads and Fr Parcel Shelf Material to rebuild my Dash Area and replace the crap Stereo Head and crap speakers.  Naturally, as we all know, one jobs leads to another !
Any help or good ideas much appreciated in advance.

I had the same problem getting blasting media out when I got the RS stripped.  i used an airgun to blow out as much as I could and directed what I could into the middle of the sill where it was easy to get a vacuum hose in by taping over some of the holes and directing the airstream from the holes at each end. Bit messy but worked, though took a couple of goes. the media grit was probably a bit finer than your sand so that might be a factor.  Sprayed the insides after with Lanotec.
Cheers, Len

Bernie, if you can't access the area after the above method, may I suggest making a hole of required diameter in an inconspicuous place. You can then fit an appropriate blanking grommet. This way you will always have access.
Just a thought. Mark

both good ideas, sure to work^^
 
or you could use it as an excuse to mount the Capri on a rotisserie and shake it out.
Then your fish oil can go in and be sure to get a good covering..

Hi Bernie
Get rid of the dust and dirt with a full restoration.
Can’t wait to read about it some time sooner than later.
Take care on the road

A shop vac with I skinny hose long enough to probe those hard to reach spots with the help of air compress the opposite direction... Or as Deano mentioned since he's seen the light with rotisserie could be a way of you've the time to build one. 👍

Thanks everyone for very good ideas  ..........   if it was only my 2nd or 3rd Classic car, I may have considered a full resto on my "Wild Plum" Special, but Im too ashamed to say how long since I was made the proud owner of a complete 1937 Oldsmobile Straight 8 and have only rebuilt the motor and tranny without installing , plus 4 new tyres and havent touched anything else. At least its been in the warm dry garage all these years ! 
I need to at least get my FLEET of Classics on the road instead of storage, and the boys can do the restos eventually as I cant see them all on the road before I "check out", but I will try by darnest !

Thanks Reeni
hope you and the family are feeling a little better after the traumatic news recently.
Best wishes from me and my family.      Stay safe always and all ways.
Kindest regards
Bernie

We’re all coping well,
Thanks.
It’s been a long time since I’ve seen the Capri
It’s with a panel beater. I’m told he’s going over the shell making all panels fit rite. When it’s off to be painted I’ll post a picture.
Would be nice before the end of this year.

So happy for you all Reeni; I've been in your position too many times. It hurts more than anything else. That's life!
All part of being human taking extreme good with extreme bad, and all in between.  Certainly confirms our mortality.
 
Hope your Capri comes back as wonderful as you hoped for; can't wait to see it.
Fingers crossed it comes back ready for driving at Christmas !
What colour are you going for Reeni ?
 
While I have my Dash all out to install all New Crash Pad and Instruments Surround, I can't ignore maintenance on Heater and 
Wiper Linkages and clean out all Ducting.  If it was my only car I would strip it 100% and "rotisserie" the lot, but I must keep
"order of priority" and get all my cars roadworthy first.  "Paint Bling" comes after all cars are roadworthy !