Certain words in the description are guaranteed to trigger an alert in the automated customs system and select it for inspection. Even if not confiscated right away, customs can still take items with them for further investigation. This will lead to either release or confiscation, but always to (sometimes long) delays.
My advice is to keep descriptions in customs declarations as general as possible. However, do not lie! Items are declared with a number from the HS (Harmonized System) Code, which can be found here: https://www.tariffnumber.com/ . Other words for these codes are Tariff Numbers, Taric Codes etc. Basically, every item known to man can be classed under one of the codes in this list. Sometimes (often!) it can be difficult to decide what class an item falls under. These codes are used world-wide. An HS Code consists of 10 numbers (0-9) and the '0', the more general the number is.
Let's take a look at that canvas GPMG cover for an example. It's a gun case/cover, which is basically a bag, made of (mainly) canvas, so look under Section VIII which includes 'travel goods, hand bags and similar containers'. Click that section, and you'll see 3 chapters listed to choose from. In this case, go for Chapter 42 and you'll see a myriad of options. Actually, there are several you could choose from (basically any that lists the outer material as fabric), but listed under option 4202 you'll find, hidden among lots of other options, the words 'gun cases' and a bit further 'of leather or textile materials', so this would be the most correct option. Click it, and again you'll get a myriad of options. Now, look for the option that lists both 'gun case' and 'outer surface of textile materials' and you'll probably land at 42029298 (blah blah gun cases blah blah with an outer surface of textile materials). This is as far as I would take it; the number given is 8 numbers so just add 2 zeros to reach a length of 10: 4202929800. Declare the GPMG cover as a 'Canvas bag' with HS Code 4202929800 and you're good to go as it perfectly fits into both description and HS Code; no need to mention 'gun', 'surplus', 'military', 'GPMG' or other scary words that might (will!) trigger an alarm.
The materials used in construction are very important. P37 packs are canvas bags for instant, and I would just declare them under HS code 42029291 (Travelling-bags, toilet bags, rucksacks and sports bags, with outer surface of textile materials). For Clansman radio parts I would try to see if they fit under Section XVI, Chapter 85, option 8517 and choose from the sub-options listed there, depending on what the item is. It doesn't have to be perfect, just close enough and remember, no need to use scary words.
The fastest way to do this is google 'HS code canvas bag' (or whatever item) and check the codes that come up in the above listed website. It might not be correct, but it probably will take you the correct chapter/section at least.
Have fun! 😆