Trailer question

OK I know its a bit off topic but I trust your collective judgment. I tow a Sankey trailer, 1965 (ish) and want to use it more when we go camping. There are times when I would like to leave it at the roadside (suitably locked) and i know it must be lit. making a light system now. I've got two red/white side marker lights and I'm going to fit one each side. with a battery. Anyone know what the relevant rules are? Height is a key question. I've just e-mailed "Ask the police" so I will tell you what they say. I fear they may not have been born when my trailer was made.

Get good locks for the wheel & hitch.
Thought you only needed O/S night lights if on a more than 30mph road
Yes to reflectors
As for the height no taller than a caravan.
If the police don't know may be highways agency
Good luck

I didnt even know it had to be lit.

Lots of caravans round and abouts not lit up at night. I presumed as long as the reflectors work and its in a 30 mph zone all was well.

I shall send them a strongly worded letter

X1 on lighting.

Well i have a chocolate tea pot of an answer from plod. The "please fill in our feeback" bit was longer than the answer:
"Thank you for your email.
You will need to comply with the relevant provisions in the Road Vehicles (Lighting) Regulations 1989 - please see the link below:
http://www.legislation.gov.uk/uksi/1989/1796/contents/made
The regulations are extremely detailed and involved. For this reason we would suggest you have the lights fitted by a reputable garage that will be familiar with all the relevant requirements and specifications.
We hope this information is of use.
Regards,
PNLD"
As my trailer is pre 85 its actually exempt a lot of the light contruction regs which means any pair of red/white makers above 400mm and below 1700mm seem to be ok. As someone referenced above, the key bit is in the highway code:
https://www.highwaycodeuk.co.uk/parking-at-night.html
Which requires lights.
Aside re the 1989 regs - it seems that pre 85 you can pretty much do what you like when it comes to rear fogs and good news for me (as I have fog on the series) is that you do not need one on the trailer (I don't) if the vehile is not required to have one (as opposed to has or has not got one),
But most useful thing to come out of this for me is the advice above to get a wheel lock, I know you are right and without that I won't be leaving my trailer anywhere, so "thank you", the lights can wait!.

Just buy a light board?

A light board won't work (I have one) for parking as its not visible from the front as well as the rear. and it needs power so I want low power LEDs.