Should there be loft insulation inside Elan sills?

[Hawksmoor]

The sills of my 1971 Elan Sprint are packed full of what looks like normal fibreglass loft insulation - the stuff that comes on rolls and is used to insulate loft spaces in houses. It goes right up front inside the body shell too.
Is this normal? If not, should there be anything in the sill voids, or are they just left open?
And I wonder whether the underfloor carpet felts are best replaced with one of the stick-on sound deadening mat products?
Many thanks in advance.

[mbell]

One of the rear wheel arch closing plates fell off on my +2. Inside was a lump of insulation material that was probably got to the plate originally.

Not fiber glass insulation and not sure what type it was but found similar stuff inside behind the side panels.

I'd guess a dpo replaced what was fitted by the factory or added some to try reduce noise.

[HCA]

By underfloor carpet felt, do you mean the original horsehair type? Stick on sound deadening mats do not come anywhere close to horsehair! Marvellous stuff!

[saildrive2001]

Mine never had any.